Image reading apparatus and image reading method

ABSTRACT

An image reading apparatus comprises a light source for repeatedly emitting first light having a first color, second light having a second color and third light having a third color toward a read target while moving the light source in a sub-scanning direction, first, second, and third sensors, each configured to sense a strength of first, second, and third reflected light, respectively, in a light reflected from the read target, and to output first, second, and third signal waveforms corresponding to the strength of the first, second, and third reflected light, respectively, and a controller. The controller is configured to execute a line-to-line correction for correcting a phase shift between the first, second, and third signal waveforms, and to correct a shift in a signal level caused by the line-to-line correction.

FIELD

Embodiments described herein relate generally to an image readingapparatus and an image reading method.

BACKGROUND

A conventional image reading apparatus reads an image on a sheet byacquiring reflected light when light of each color including red, greenand blue is irradiated by a light source onto a read target, such as asheet. In this case, the light source moves in a sub-scanning directionand sequentially switches among red, green and blue light to emit thelight of different color to the sheet at different times. Since thelight source moves in the sub-scanning direction during the switching,light of different color is irradiated onto different positions of thesheet. For this reason, instead of reading an image with the red, greenand blue light overlapped with each other, the image is read with colorshifting. In view of such a problem, there is a method of converting theacquired reflected light to an electric signal indicating a strength ofthe reflected light, and correcting a phase of the electric signal. Bycorrecting the phase of the electric signal, the color shift iscorrected, and an image that is close to the image that is read when thered, green and blue light is emitted to the same position on the sheet,can be acquired. However, in the conventional method, although the imageread by the image reading apparatus is an image in which the color shiftis corrected, there is a case in which a color of the image is changed.The change of color refers to that a color of the image read by theimage reading apparatus is different from the color of the read target.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of an image reading apparatus according to anembodiment;

FIG. 2 is a schematic diagram of different elements of an image readingsection of the image reading apparatus;

FIG. 3 is a diagram illustrating an example of hardware structures of aCCD sensor and a CCD substrate according to the embodiment;

FIG. 4 is a diagram illustrating an example of a hardware structure asseen from the front of the CCD sensor according to the embodiment;

FIG. 5 is a diagram illustrating an example of functional components ofa signal processing section according to the embodiment;

FIG. 6 is a diagram illustrating an example of strength information;

FIG. 7 is a diagram illustrating an example of a phase difference amongsignals of a red signal string, a blue signal string, and a green signalstring;

FIG. 8 is a diagram illustrating a line-to-line correction section thatgenerates a signal level difference;

FIG. 9 is a flowchart illustrating an example of a process flow in whichthe image reading apparatus performs a correction among signal stringsaccording to the embodiment; and

FIG. 10 is a diagram illustrating an example of each signal string aftercorrection by the line-to-line correction section and the signal levelcorrection section is executed according to the embodiment.

DETAILED DESCRIPTION

In accordance with an embodiment, an image reading apparatus comprises alight source, an acquisition section, a first correction section, and asecond correction section. The light source configured to repeatedlyemit first light having a first color, second light having a secondcolor and third light having a third color at different times toward aread target while moving the light source in a first direction, first,second, and third sensors, each configured to sense a strength of first,second, and third reflected light, respectively, in a light reflectedfrom the read target, and to output first, second, and third signalwaveforms, respectively, the first signal waveform corresponding to thestrength of the first reflected light sensed by the first sensor, thesecond signal waveform corresponding to the strength of the secondreflected light sensed by the second sensor, and the third signalwaveform corresponding to the strength of the third reflected lightsensed by the third sensor, and a controller. The controller isconfigured to execute a line-to-line correction for correcting a phaseshift between the first, second, and third signal waveforms, and tocorrect a shift in a signal level caused by the line-to-line correction.

Hereinafter, an image reading apparatus and an image reading method ofan embodiment are described with reference to the accompanying drawings.

FIG. 1 is an external diagram exemplifying the entire configuration ofan image reading apparatus 100 according to the embodiment. The imagereading apparatus 100 is, for example, an image forming apparatus suchas a multi-functional peripheral. The image reading apparatus 100 isprovided with a display 110, a control panel 120, a printer section 130,a sheet housing section 140 and an image reading section 200. Theprinter section 130 of the image reading apparatus 100 may be a devicethat performs printing by fixing a toner image or an inkjet typeprinting device.

The image reading apparatus 100 reads an image displayed on a sheet andgenerates digital data to generate an image file. The sheet is, forexample, an original document and a paper on which characters or imagesare recorded. Instead of a sheet, other objects may be the read targetas long as it can be read by the image reading apparatus 100. In thepresent embodiment, for the purpose of simplicity, it is assumed thatthe image reading apparatus 100 reads the image on the sheet as a grayscale image.

The display 110 is an image display device such as a liquid crystaldisplay, an organic EL (electro luminescence) display or the like. Thedisplay 110 displays various kinds of information relating to the imagereading apparatus 100.

The control panel 120 has a plurality of buttons. The control panel 120receives an operation by a user. The control panel 120 outputs a signalin response to an operation carried out by the user to a controller ofthe image reading apparatus 100. The control panel 120 and the display110 are integrated as a touch panel.

The printer section 130 forms an image on a sheet according to imageinformation generated by the image reading section 200 or imageinformation received via a communication path. The printer section 130forms an image through, for example, the following process. An imageforming section of the printer section 130 forms an electrostatic latentimage on a photoconductive drum based on the image information. Theimage forming section of the printer section 130 attaches a developingagent to the electrostatic latent image to form a visible image. A toneris an example of the developing agent. A transfer section of the printersection 130 transfers the visible image onto the sheet. A fixing sectionof the printer section 130 heats and pressurizes the sheet to fix thevisible image on the sheet. The sheet on which an image is formed may bea sheet accommodated in the sheet housing section 140 or a manually fedsheet.

The sheet housing section 140 accommodates the sheet used for the imageformation carried out by the printer section 130.

The image reading section 200 reads the image information from a readtarget as intensity of light. The image reading section 200 records theread image information. The recorded image information may be sent toother image processing apparatus via a network. The recorded imageinformation may be used to form an image on the sheet by the printersection 130.

FIG. 2 is a schematic diagram of different elements of the image readingsection 200.

The image reading section 200 is provided with a document table 20, afirst carriage 21, a second carriage 22, an image capturing section 23,an operation controller 24 and a signal processing section 25. Thedocument table 20 may be a part of an ADF (Automatic Document Feeder). Adirection in which the first carriage 21 moves is a sub-scanningdirection Y. In the document table 20, a direction orthogonal to thesub-scanning direction Y is a main scanning direction X. A directionorthogonal to the main scanning direction X and the sub-scanningdirection Y is a height direction Z.

The document table 20 includes a document table glass 201, a shadingplate 202, a document scale 203 and a transparent glass 204.

The document table glass 201 has a placing surface 201 a on which asheet S is placed. The shading plate 202 includes a member with areference color by which shading correction is carried out on an imageread (hereinafter, referred to as a “read image”) from the sheet S. Forexample, the shading plate 202 has white color. The shading plate 202 isrectangular and has long sides in the main scanning direction X. Thedocument scale 203 indicates a position of the sheet S placed on thedocument table glass 201. A tip reference section 203 a is arranged atan end of the document scale 203. The tip reference section 203 a isformed with a difference in height with respect to the placing surface201 a of the document table glass 201 to form a convex portion againstwhich the end of the sheet S is pressed. The sheet S is pressed againstthe tip reference section 203 a on the document table glass 201 and thusa position thereof is determined. A position at which corners of tips ofthe sheet S are to be placed is thus predetermined on the placingsurface 201 a. Accordingly, the positions in the main scanning directionX and the sub-scanning direction Y are determined by placing the cornersof the tips of the sheet S at the predetermined positions.

The first carriage 21 is provided with a light source 211, a reflector212 and a first mirror 213.

The light source 211 emits the light of each color including red (R),green (G) and blue (B) at a predetermined time interval dt in the orderof red, green and blue. For example, the light source 211 emitting thered light at a time t0 emits the green light at a time t1 which is atime dt later than the time t0. The light source 211 emitting the greenlight at the time t1 emits the blue light at a time t2 which is the timedt later than the time t1. Furthermore, at a time t2, the light source211 emitting the blue light emits the red light at a time t3 which isthe time dt later than the time t2. The time t0, t1, t2, t3 and dt havethe following relationship: t1=t0+dt, t2=t1+dt=t0+2*dt, and t3=t0+3*dt.The light source 211 repeats the operations performed from t0 to t3after the time t3. Below, the operation of the light source 211 fromemission of the red light to emission of the blue light is referred toas a unit operation. The time required by one unit operation is a fixedtime of t3-t0. Below, among the unit operations performed after thepredetermined time, which is for example a time at which the lightsource 211 is energized to start operating, the unit operation of Nthtime is referred to as a unit operation N.

The reflector 212 reflects the light emitted from the light source 211.The light reflected by the reflector 212 is emitted to the shading plate202 and the sheet S uniformly. Light distribution characteristics in themain scanning direction X at a reading position in the sub-scanningdirection of the sheet S are adjusted based on the reflected light ofthe emitted light. The first mirror 213 reflects the light reflected bythe shading plate 202 and the sheet S towards a second mirror 221 of thesecond carriage 22.

The second carriage 22 is provided with the second mirror 221 and athird mirror 222. The second mirror 221 reflects the light reflected bythe first mirror 213 towards the third mirror 222. The third mirror 222reflects the light reflected by the second mirror 221 to a condenserlens 231 of the image capturing section 23.

The image capturing section 23 is provided with the condenser lens 231,a CCD (Charge Coupled Device) sensor 232 and a CCD substrate 233. Thecondenser lens 231 condenses the light reflected by the third mirror222. The condenser lens 231 directs the condensed light to be imaged onan imaging plane of the CCD sensor 232. The CCD sensor 232 is installedon the CCD substrate 233. The CCD sensor 232 includes, for example,three line sensors for reading a color image. The line sensor is asensor in which a plurality of CCDs is arranged in a row in the mainscanning direction. In the present embodiment, the CCDs are arranged inan X-axis direction in FIG. 2. The line sensor outputs a signalindicating strength of the light received by each CCD. The CCD sensor232 reads R (red) light, G (green) light and B (blue) light. The CCDsensor 232 converts the light imaged by the condenser lens 231 into anelectric charge. Through the conversion, the CCD sensor 232 converts animage formed by the condenser lens 231 to an electrical signal. The CCDsubstrate 233 converts the electrical signal generated by aphotoelectric conversion of the CCD sensor 232 to a digital signal. TheCCD substrate 233 outputs the generated digital signal to the signalprocessing section 25. The foregoing processing carried out by the CCDsubstrate 233 is executed by an AFE (Analog Front End) circuit installedon the CCD substrate 233.

FIG. 3 is a diagram illustrating an example of the hardware structuresof the CCD sensor 232 and the CCD substrate 233 according to theembodiment.

The CCD sensor 232 includes three line sensors, i.e., a red line sensor232-R, a green line sensor 232-G, and a blue line sensor 232-B. Each CCDof the red line sensor 232-R outputs an analog signal indicating thestrength of the R (red) light in the light received thereby(hereinafter, referred to as “red analog signal”). Each CCD of the greenline sensor 232-G outputs an analog signal indicating the strength ofthe G (green) light in the light received thereby (hereinafter, referredto as “green analog signal”). The blue line sensor 232-B outputs ananalog signal indicating the strength of the B (blue) light in the lightreceived thereby (hereinafter, referred to as “blue analog signal”).

In place of the CCD, the line sensor may employ any type of solid-stateimage capturing element that generates electric charge from lightreceived thereby. For example, the line sensor may employ a CMOS(Complementary metal-oxide-semiconductor) instead of the CCD.

The CCD substrate 233 includes an AFE circuit 2331. The AFE circuit 2331acquires a red analog signal and converts it to a red digital signal.The AFE circuit 2331 acquires the green analog signal and converts it toa green digital signal. The AFE 2331 acquires the blue analog signal andconverts it to a blue digital signal. Hereinafter, the red digitalsignal, the green digital signal, and the blue digital signal arereferred to as a light strength digital signal if they are notdistinguished.

FIG. 4 is a diagram illustrating an example of the hardware structure asseen from the front of the CCD sensor 232 according to the embodiment.The CCD sensor 232 includes the red line sensor 232-R, the green linesensor 232-G, and the blue line sensor 232-B. Each CCD of a unit CCDgroup, which is made up of one CCD of the redline sensor 232-R, one CCDof the green line sensor 232-G and one CCD of the blue line sensor 232-Bhaving the same X coordinate position, receives red reflected light,green reflected light, and blue reflected light respectively in the sameunit operation. Specifically, in FIG. 4, three CCDs included in an area901 constitute one unit CCD group. Also, the three CCDs existing in anarea 902 constitute another unit CCD group. Below, the unit CCD groupexisting in the area 901 is referred to as unit CCD group 901, and theunit CCD group existing in the area 902 is referred to as unit CCD group902. Each adjacent unit CCD group receives the light reflected bymutually adjacent reading positions in the main scanning direction. Morespecifically, the reading position on the sheet S reflecting the lightreceived by the unit CCD group 901 is adjacent to the reading positionon the sheet S that reflects the light received by the unit CCD group902.

Returning to the description in FIG. 2. The operation controller 24controls the first carriage 21, the second carriage 22 and the imagecapturing section 23. For example, the operation controller 24 controlsthe movement of the first carriage 21 and the lighting and extinction ofthe light source 211 of the first carriage 21. For example, theoperation controller 24 controls the operations of the image capturingsection 23.

The operation controller 24 controls the state of the image readingapparatus 100 to be either of a normal state and a low-power state. Thenormal state is a state in which the image reading apparatus 100 iscapable of reading an image of an original document in response to theinstruction of the user. In the normal state, a timing generatorinstalled on the CCD substrate 233 outputs a CCD control signal to theCCD sensor 232. The low-power state is a state in which the imagereading apparatus 100 is incapable of reading the image of the documentin response to the instruction by the user, and thus power consumptionin the low-power state is lower than that in the normal state. In thelow-power state, the timing generator installed on the CCD substrate 233stops. Thus, in the low-power state, the CCD control signal cannot beoutput. Thus, the operation of the CCD sensor 232 stops.

The first carriage 21 moves in the sub-scanning direction Y under thecontrol of the operation controller 24. The second carriage 22 moves ata half speed in the same direction as the first carriage 21 along withthe movement of the first carriage 21. Through such a movement, even ifthe first carriage 21 moves, an optical path length of the lightreaching the imaging plane of the CCD sensor 232 does not vary. In otherwords, the optical path length of the light in an optical systemcomposed of the first mirror 213, the second mirror 221, the thirdmirror 222 and the condenser lens 231 is constant. The optical pathlength from the placing surface 201 a to the imaging plane of the CCDsensor 232 is thus constant

For example, as shown in FIG. 2, the first carriage 21 moves from leftto right along the sub-scanning direction Y at a constant speed. As thefirst carriage 21 moves in the sub-scanning direction Y, a readingposition P of the sub-scanning direction of the sheet S moves as well.Thus, the reading position P of the sub-scanning direction moves fromleft to right along the sub-scanning direction Y. The reading position Pof the sub-scanning direction is a position corresponding to one line ofthe main scanning direction X. Through the movement of the readingposition P of the sub-scanning direction in the sub-scanning directionY, images of the reading positions P of the sub-scanning direction ofthe sheet S are sequentially formed on the imaging plane of the CCDsensor 232. The CCD sensor 232 outputs a signal corresponding to theformed image at the reading position P as a signal corresponding to oneline of the main scanning direction X. The CCD substrate 233 generatesimage data of the whole sheet S on the basis of signals corresponding toa plurality of lines.

The signal processing section 25 acquires the red digital signal, thegreen digital signal, and the blue digital signal output from the imagecapturing section 23 and outputs image data on which digital signalprocessing such as line-to-line correction is performed on the acquiredsignal.

FIG. 5 is a diagram illustrating an example of the functional componentsof the signal processing section 25 according to the embodiment. Thesignal processing section 25 includes a processor (not shown) and acorrection memory 251 connected by a bus line (not shown), and executesa program. The signal processing section 25 executes a program toimplement a line-to-line correction section 252 and a signal levelcorrection section 253. Alternatively, all or a part of functions of thesignal processing section 25 may be realized by using hardware such asan ASIC (Application Specific Integrated Circuit), a PLD (ProgrammableLogic Device) or an FPGA (Field Programmable Gate Array). The programmay be recorded in a computer-readable recording medium. Thecomputer-readable recording medium is, for example, a portable mediumsuch as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM or thelike, or a storage device such as a hard disk built in a computersystem. The program may be transmitted via an electric communicationline.

The correction memory 251 stores values indicating the strength of thelight indicated by the light strength digital signal for each unitoperation and unit CCD group. Hereinafter, information indicating thestrength of the light indicated by the light strength digital signal foreach unit CCD group is referred to as strength information.

FIG. 6 is a diagram illustrating an example of the strength informationaccording to the embodiment. For example, the strength information isstored in the correction memory 251 as a strength information table 911shown in FIG. 6 for each CCD group. The correction memory 251 has arecord for each operation number. Each record has an operation numberand values of the red strength, the green strength and the bluestrength. The operation number indicates the order of the unitoperation. The operation number correlates with the reading position Pof the sub-scanning direction on the sheet S. The value of the operationnumber is also the number of times the unit operation has been repeatedfrom the start of the first unit operation in a certain readingoperation until the unit operation in the order indicated by theoperation number is completed. As described above, the time taken forone unit operation is always constant. Therefore, the value of theoperation number is proportional to the time from the start of the firstunit operation to the end of the unit operation of the operation number.In addition, the reading position P of the sub-scanning direction on thesheet S moves along with the movement of the light source 211. Since thelight source 211 moves in the sub-scanning direction at a constantspeed, the reading position P on the sheet S also moves on the sheet Sin the sub-scanning direction at a constant speed. Therefore, thereading position P in the sub-scanning direction on the sheet S isproportional to the time with a time at which the light source 211starts moving set as a time origin. The image reading apparatus 100correlates the time at which the light source 211 starts moving and thetime at which the unit operation starts since the light source 211 readsthe sheet S by performing the movement and the unit operation.

Red strength has a value indicating the strength of the red reflectedlight acquired by the unit CCD group 901 in the unit operation in theorder indicated by the operation number. Green strength has a valueindicating the strength of the green reflected light acquired by theunit CCD group 901 in the unit operation in the order indicated by theoperation number. Blue strength has a value indicating the strength ofthe blue reflected light acquired by the unit CCD group 901 in the unitoperation in the order indicated by the operation number.

For example, a record 9111 indicates that the strength of the redreflected light, the green reflected light and the blue reflected lightacquired by the unit CCD group 901 is 170, 180 and 192 in the fifth unitoperation of the light source 211.

Each value of the strength information table 911 is indicated by 8 bitsand stored in a memory area of the correction memory 251.

The values of the red strength, the green strength and the blue strengthin the strength information table 911 are output to the line-to-linecorrection section 252 and the signal level correction section 253 inthe order of the operation number. Hereinafter, a signal stringindicating a series of red strength values output in order of theoperation number is called a red signal string. A signal level of thered signal string indicates the red strength. Hereinafter, a signalstring indicating a series of green strength values output to theline-to-line correction section 252 and the signal level correctionsection 253 in the order of operation number is called a green signalstring. The value indicated by the signal level of the green signalstring is the value indicated by the green strength. Hereinafter, asignal string indicating a series of blue strength values output to theline-to-line correction section 252 and the signal level correctionsection 253 in the order of the operation number is called a blue signalstring. A signal level of the blue signal string indicates the bluestrength.

Returning to the description in FIG. 5, the line-to-line correctionsection 252 corrects a phase difference among signal strings based onthe red signal string, the green signal string and the blue signalstring.

The phase difference in the present embodiment means a shift betweenwaveforms of the signal strings. Correcting the phase difference in thepresent embodiment refers to reducing the shift.

The phase difference is caused by continuous movement in thesub-scanning line direction of the light source 211 even during the unitoperation. Since the light source 211 continues to move during the unitoperation, positions (hereinafter, referred to as “reflectionpositions”) on the sheet from which the red light, the green light andthe blue light emitted by the light source 211, are reflected aredifferent for each color. Therefore, the phase difference occurs amongthe signal strings. Below, the phase difference is described in moredetail.

If the image reading apparatus 100 reads the sheet S without moving thelight source 211 in the unit operation, the light of the three colorsemitted by the light source 211 in the unit operation are reflected atone reflection position on the sheet S. In that case, the image readingapparatus 100 reads one reflection position on the sheet S in one unitoperation. The value of the red strength, the green strength or the bluestrength in each record of the strength information table 911 indicatesthe strength of the light reflected at the same reflection position onthe sheet S for each record. Therefore, since the image readingapparatus 100 reads a grayscale image, the strength indicated by the redstrength, the green strength and the blue strength is substantially thesame strength within the same record.

However, actually, in order to reduce the reading time, the imagereading apparatus 100 reads the sheet S while moving the light source211 even during the unit operation. The image reading apparatus 100 thusreads the sheet S based on light of the three colors being emitted ontodifferent positions on the sheet S. The reflection positions of thelight of the three colors are positions shifted according to themovement speed of the light source 211. The values of the red strength,the green strength and the blue strength in each record of the strengthinformation table 911 indicate the strength of the light reflected atthe reflection positions that are shifted from each other even withinthe same record. Therefore, the red strength, the green strength and theblue strength are shifted even within the same record. Due to the shiftin the strength, a change method of the signal level along the operationnumber of the signal level varies among the signal strings. Therefore,the operation numbers having predetermined signal levels are differentamong the signal strings in some cases. The difference in the operationnumbers among the signal strings is called the phase difference.

Since the reading position in the sub-scanning direction correlates withthe operation number, the reflection position correlates to theoperation number. Each signal string indicates the strength of eachreflected light at each reflection position.

FIG. 7 is a diagram illustrating an example of the phase differenceamong the signals of the red signal string, the blue signal string, andthe green signal string according to the embodiment. In FIG. 7, thehorizontal axis represents the operation number. The vertical axisrepresents the signal level of each signal string. As shown in FIG. 7,the change of the signal levels of the red signal string, the greensignal string and the blue signal string is different. Therefore, thereis the phase difference among the signal strings.

As described above, the light source 211 of the image reading apparatus100 continues to move in the sub-scanning direction even in the unitoperation, thereby generating the phase difference among the signalstrings.

Returning to the description in FIG. 5, the line-to-line correctionsection 252 reduces the phase difference among the signal strings.Specifically, the line-to-line correction section 252 performs aline-to-line correction on the two signal strings of the three signalstrings to reduce the phase difference with a reference signal string.The reference signal string is a signal string of the remaining one ofthe three signal strings, on which no line-to-line correction isexecuted. The reference signal string is a signal string predeterminedto be not subjected to the line-to-line correction. The line-to-linecorrection is a processing to correct the signal level in each operationnumber of each signal string. The line-to-line correction is performedin the following manner: (1) a value obtained by multiplying the signallevel at the preceding and succeeding operation numbers by thepredetermined first and second correction coefficients is outputted; (2)a value obtained by multiplying its own value by a predetermined thirdcorrection coefficient is outputted; and (3) calculate the average valueof (1) and (2).

Since the line-to-line correction is performed using the first to thethird correction coefficients, the change in the signal level of thesignal string occurs. Therefore, although the phase difference among thesignal strings decreases due to the line-to-line correction by theline-to-line correction section 252, there is a case in which differenceoccurs in the signal level among the signal strings.

The line-to-line correction section 252 outputs the corrected signalstring to an image processing section (not shown) provided in the imagereading apparatus 100 at a rear stage. The image processing section (notshown) is realized by using hardware such as an ASIC, a PLD, an FPGA, orthe like, and executes an image processing.

FIG. 8 is a diagram illustrating that the line-to-line correctionsection 252 generates the signal level difference according to theembodiment. FIG. 8 shows a signal string after the line-to-linecorrection section 252 performs the line-to-line correction for the redsignal string and the blue signal string with the green signal string inFIG. 7 as the reference signal string. FIG. 8 shows a case in which thephase difference among the signal strings after the line-to-linecorrection is executed is smaller compared with that in FIG. 7. However,FIG. 8 shows a case in which the signal level difference among thesignal strings occurs due to the line-to-line correction. Morespecifically, FIG. 8 shows a case in which the difference occurs betweenthe signal levels of the red signal string and the blue signal string onwhich the line-to-line correction is performed and the signal level ofthe green signal string that is the reference signal string. The signallevels of the red signal string and the blue signal string subjected tothe line-to-line correction processing are about the same.

Returning to the description in FIG. 5. The signal level correctionsection 253 corrects the signal level difference among the signalstrings caused by line-to-line correction section 252. Morespecifically, the signal level correction section 253 corrects thesignal level of the reference signal string by a predetermined value(hereinafter, referred to as a “level correction coefficient”). Forexample, by multiplying the signal level of the reference signal stringby the predetermined level correction coefficient, the signal level ofthe reference signal string is corrected. The predetermined levelcorrection coefficient may be any value as long as it can correct thesignal level. For example, the level correction coefficient may be apredetermined value based on the reflected light at a predeterminedposition (hereinafter, referred to as “reference position”) on apredetermined sheet (hereinafter, referred to as “reference sheet”). Forexample, the color of the reference position on the reference sheet maybe any color as long as the reflectance for light of each color of RGBis substantially the same. For example, the color of the referenceposition on the reference sheet is a harmony color such as gray scale.

The signal level correction section 253 acts as a digital filter. Thesignal level correction section 253 corrects the signal level of thereference signal string based on the level correction coefficient whichis a predetermined fixed value regardless of the result of theline-to-line correction by the line-to-line correction section 252.Therefore, the signal level correction section 253 does not necessarilycorrect the reference signal string after the line-to-line correctionsection 252 performs the correction. The signal level correction section253 may correct the reference signal string in parallel with the linecorrection section 252. In the present embodiment, the signal levelcorrection section 253 is corrected in parallel with the line-to-linecorrection section 252.

The line-to-line correction section 253 outputs the corrected signalstring to the image processing section (not shown) provided in the imagereading apparatus 100 at the rear stage.

FIG. 9 is a flowchart illustrating an example of a process flow in whichthe image reading apparatus 100 executes the correction among the signalstrings according to the embodiment.

The image reading apparatus 100 corrects the phase difference among thesignal strings by executing the line-to-line correction by theline-to-line correction section 252 (ACT 101). Specifically, theline-to-line correction section 252 performs correction with the greensignal string as the reference signal string. More specifically, theline-to-line correction section 252 performs the line-to-line correctionon the red signal string and the blue signal string so that the phasedifference between the red signal string and the green signal string andthe phase difference between the blue signal string and the green signalstring are reduced.

The image reading apparatus 100 changes the signal level differenceamong the signals by the signal level correction section 253 in parallelwith the processing in which the line-to-line correction section 252performs the correction (ACT 102). Specifically, the signal levelcorrection section 253 changes the signal level difference among thesignal strings by multiplying the signal level of the green signal whichis the reference signal string by the level correction coefficient whichis a predetermined fixed value. As a result of the correction, thesignal level of the corrected green signal string becomes substantiallythe same signal level as the red signal string and the blue signalstring on which the line-to-line correction is performed.

The image reading apparatus 100 outputs the red signal string and theblue signal string corrected by the line-to-line correction section 252and the green signal string corrected by the signal level correctionsection 253 to the image processing section (not shown) at the rearstage.

FIG. 10 is a diagram illustrating an example of each signal string aftercorrection by the line-to-line correction section 252 or the signallevel correction section 253 for each signal string in FIG. 7.

The phase difference and the signal level difference among the signalsin FIG. 10 are smaller compared with the phase difference among thesignal strings in FIG. 7 and the signal level difference among thesignal strings in FIG. 8.

The image reading apparatus 100 of the embodiment configured in this wayis provided with the signal level correction section 253, thereby makingit possible to reduce the signal level difference among the signalsgenerated by the line-to-line correction and suppress the change incolor.

The light source 211 may emit the light in an order that is differentfrom the order of red, blue and green. For example, the light source 211may emit the light in the order of blue, green and red.

The reference signal string need not necessarily be the green signalstring. The reference signal string may be the red signal string or theblue signal string. However, by setting the signal string correspondingto the color of the light emitted second among the light of the threecolors sequentially emitted by the light source 211 as the referencesignal string, it is possible to reduce the phase difference required tobe subjected to the line-to-line correction. Therefore, by using thesignal string corresponding to the color of the light emitted secondamong the light of the three colors sequentially emitted by the lightsource 211 as the reference signal string, the accuracy of thecorrection can be improved.

The line-to-line correction section 252 does not necessarily need toperform the line-to-line correction on only two signal strings otherthan the reference signal. The line-to-line correction section 252 mayperform the line-to-line correction for all three signal strings. If theline-to-line correction section 252 performs the line-to-line correctionfor all three signal strings, the signal level correction section 253performs the correction after correction by the line-to-line correctionsection 252. Furthermore, in this case, the signal level correctionsection 253 may correct two or more signal strings.

In addition, the line-to-line correction section 252 may perform theline-to-line correction only for one signal string.

In the embodiments described above, the signal level correction section253 corrects only the reference signal string. In other embodiments, thesignal level correction section 253 may correct all or a part of thesignal strings corrected by the line-to-line correction section 252. Inthis case, the signal level correction section 253 carries out thecorrection on the signal string corrected by the line-to-line correctionsection 252 after the correction by the line-to-line correction section252 is performed.

The signal processing section 25 does not need to be implemented asindependent hardware. For example, the signal processing section 25 maybe provided on the CCD substrate 233.

The image reading apparatus 100 may read an image on one side of thesheet or on both sides of the sheet.

The image reading apparatus 100 may read a color image in addition tothe grayscale image. Also in that case, the signal level correctionsection 253 corrects the signal level of each signal string bymultiplying the signal level of each signal string by the predeterminedlevel correction coefficient.

The signal level correction section 253 may correct the signal leveldifference among the signal strings by addition or subtraction insteadof by multiplication.

The number of AFE circuit 2331 is not necessarily one, and AFE circuitsmay be respectively provided for each sensor of the red line sensor232-R, the green line sensor 232-G and the blue line sensor 232-B.

The CCD sensor 232 and the CCD substrate 233 are an example of anacquisition section. The red line sensor 232-R, the green line sensor232-G and the blue line sensor 232-B are examples of first, second andthird sensors, respectively. The red analog signal, the green analogsignal and the blue analog signal are examples of first, second andthird signals, respectively. The red signal string, the green signalstring, and the blue signal string are examples of first, second andthird signal strings, respectively. The line-to-line correction section252 is an example of a first correction section. The signal levelcorrection section 253 is an example of a second correction section.Furthermore, the level correction coefficient is an example of aparameter.

According to at least one embodiment described above, by including thesignal level correction section 253, it is possible to reduce the signallevel difference among the signals caused by the line-to-line correctionand suppress the change in color.

While certain embodiments have been described these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms: furthermore variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. An image reading apparatus, comprising: a lightsource configured to repeatedly emit first light having a first color,second light having a second color different from the first color, andthird light having a third color different from the first and secondcolors, at different times toward a read target while moving in a firstdirection; first, second, and third sensors, each configured to sense astrength of the first, second, and third lights, respectively, reflectedfrom the read target, and to output first, second, and third signalwaveforms, respectively, the first signal waveform corresponding to thestrength of the first light sensed by the first sensor, the secondsignal waveform corresponding to the strength of the second light sensedby the second sensor, and the third signal waveform corresponding to thestrength of the third light sensed by the third sensor; and a controllerconfigured to execute a line-to-line correction for correcting a phaseshift on the first and third signal waveforms, and to correct a shift ina signal level of the second signal waveform caused by the line-to-linecorrection.
 2. The image reading apparatus according to claim 1, whereinthe controller is configured to execute the line-to-line correction andcorrect the shift in the signal level, in parallel.
 3. The image readingapparatus according to claim 1, wherein the controller is configured tocorrect the shift in the signal level after executing the line-to-linecorrection.
 4. The image reading apparatus according to claim 1, whereinthe first color, the second color, and the third color are red, green,and blue, respectively, and the first, second, and third sensors, are ared light sensor, a green light sensor, and a blue light sensor,respectively.
 5. The image reading apparatus according to claim 1,wherein the first sensor, the second sensor, and the third sensor eachinclude a plurality of solid-state image capturing elements arranged ina row along a second direction that is perpendicular to the firstdirection.
 6. The image reading apparatus according to claim 1, whereinduring a current light emission period, the first light is emitted afirst time interval after the third light was emitted during a priorlight emission period, the second light is emitted a second timeinterval after the first light is emitted, and the third light isemitted a third time interval after the second light is emitted, and thefirst, second, and third time intervals are all equal and a movementspeed of the light source in the first direction is constant.
 7. Animage reading method, including: repeatedly emitting first light havinga first color, second light having a second color different from thefirst color, and third light having a third color different from thefirst and second colors, at different times toward a read target whilemoving a light emission source in a first direction; acquiring first,second, and third signal waveforms corresponding to a strength of thefirst, second, and third lights, respectively, reflected from the readtarget; executing a line-to-line correction for correcting a phase shifton the first and third signal waveforms, and correcting a shift in asignal level of the second signal waveform caused by the line-to-linecorrection.
 8. The method according to claim 7, wherein the line-to-linecorrection is executed in parallel with the correction in the shift inthe signal level.
 9. The method according to claim 7, wherein the shiftin the signal level is corrected after the line-to-line correction isexecuted.
 10. The method according to claim 7, wherein the first color,the second color, and the third color are red, green, and blue,respectively, and the first, second, and third signal waveforms areacquired using a red light sensor, a green light sensor, and a bluelight sensor, respectively.
 11. The method according to claim 10,wherein the red light sensor, the green light sensor, and the blue lightsensor each include a plurality of solid-state image capturing elementsarranged in a row along a second direction that is perpendicular to thefirst direction.
 12. The method according to claim 7, wherein during acurrent light emission period, the first light is emitted a first timeinterval after the third light was emitted during a prior light emissionperiod, the second light is emitted a second time interval after thefirst light is emitted, and the third light is emitted a third timeinterval after the second light is emitted, and the first, second, andthird time intervals are all equal and a movement speed of the lightemission source in the first direction is constant.